This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2001-355821 filed on Nov. 21, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel injection pump for an internal combustion engine (hereinafter called xe2x80x9cenginexe2x80x9d).
2. Description of the Prior Art
Conventionally, a common rail fuel injection system is known typically as a system for supplying fuel to a diesel engine. The common rail fuel injection system is provided with a fuel injection pump in which plungers as moving members make reciprocating movement according to rotation of a drive shaft so that fuel supplied to pressure chambers are pressurized by the plungers. When pressure of the pressurized fuel reaches a given value, the pressurized fuel is discharged from each of the pressure chambers to a common rail.
In a case of the fuel injection pump mentioned above, a housing, in which the pressure chambers are formed in cooperation with the plungers, is equipped with a feed pump for supplying fuel to the pressure chambers. The feed pump is arranged at an end of the drive shaft, which reciprocatingly drives the plungers, and is driven according to rotation of the drive shaft so that fuel stored in a fuel tank is delivered to the pressure chambers.
In the conventional fuel injection pump, a fuel filter provided in the fuel tank eliminates foreign material contained in the fuel. Further, a filter element arranged in the housing of the fuel injection pump on a side of the fuel inlet port serves to eliminate foreign material produced in a fuel delivery pipe extending from the fuel tank to the feed pump and foreign material produced from the fuel filter itself before these foreign material flow into the feed pump.
However, the housing of the fuel injection pump does not have enough space to mount the filter element in view of conventional shape of the fuel injection pump. Accordingly, the filter element is relatively compact so that mesh size of the filter element has to be relatively large to reduce pressure loss of fuel passing though the filter element. The filter element whose mesh size is large can not eliminate minute foreign material, so efficiency of filtrating the foreign material is not high. If the foreign material having passed through the filter element enters various sliding portions formed in the fuel injection pump, the foreign material is apt to hinder smooth operation of the sliding portions, thereby the fuel injection pump has a risk of jeopardizing highly accurate fuel amount control.
Further, the conventional filter element is installed typically in a passage formed in the housing of the fuel injection pump. Accordingly, it is difficult and troublesome to replace the filter element positioned in the passage.
An object of the present invention is to provide a fuel injection pump in which minute foreign material is eliminated without causing significant pressure loss, which enables highly accurate fuel flow control and in which a fuel member is easily replaced.
To achieve the above object, in the fuel injection pump, a casing fixed to an outer surface of a housing is provided at a position adjacent to the housing with a pump room and at a position remote from the housing with a filter room mostly separated from but partly communicating with the pump room. An axial end of a drive shaft protrudes into the pump room. A feed pump is constituted by the pump room where a feed pump mechanism is connected with the axial end of the drive shaft. A filter element is accommodated in the filter room. A casing cover attached to the casing has a fuel inlet port through which fuel is sucked to the filter room and, then, flows via the filter element into the pump room where fuel is pressurized according to rotation of the drive shaft. Accordingly, foreign material contained in fuel is eliminated before entering the pump room.
The filter element is accommodated in the filter room of the casing at the position remote from the housing so that the filter element is easily replaced, for example, for a maintenance purpose by detaching the casing cover from the casing. It is preferable, therefore, that the casing cover is attached to the casing, for example, by bolts, so that the casing cover may be easily detached therefrom.
Since the filter room is formed in the casing at the position remote from the housing and there is no size limitation of inner space of the filter room, the inner space of the filter room can be sufficiently large to accommodate larger size of the filter element.
It is preferable that fuel flow area of the fuel element is larger than that of the fuel inlet port.
Further, preferably, the pump and filter rooms are formed substantially in column shape and inner diameter of the filter room is substantially equal to that of the pump room.
Employment of the larger size of the filter element results in less pressure loss of fuel passing through the filter element even if mesh size of the filter element is smaller. Since foreign material, even if it is minute, is eliminated by the filter element, there is few foreign material entering sliding portions of the fuel injection pump, which enables highly accurate fuel flow control of the fuel injection pump.
Moreover, it is preferable that the casing is composed of a cylindrical casing body and a partition dividing axially inner space of the casing body into two spaces that constitute the pump and filter rooms, respectively. Preferably, the partition has a communication hole through which the filter room communicates with the pump room. The casing mentioned above has a simpler construction in which the casing can be easily fixed to the housing and the feed pump mechanism and the filter element can be easily assembled thereto.